Relationship between Corn Yield and Plant Potassium

Chemical composition of the sixth corn (Zea mays L.) leaf at early tassel has been widely used in diagnosing the nutritional status of the plant at this particular stage of development. However at this relatively late stage of development, application of supplement plant nutrients when needed, is difficult. Thus, critical nutrient values for corn and other crop plants should be determined so that a knowledgeable interpretation of their chemical composition can be made at an early stage of development which would permit supplementary nutrient applications. Under some conditions and for some nutrients, plant uptake of one or more nutrients may be more important than concentration; “critical” uptake values should also be determined. The objective of this experiment was to determine the relationship between corn yield and the K composition of corn plants at three stages of growth where K composition includes both its concentration and uptake. Corn yields and plant samples were obtained from an experiment at the U. of III. Agron. Res. Cen. at Browns-town in South Central Illinois. Experimental plots were lanted in 76-cm rows to a population of 49,000 plants/ha of an Illinois-adapted cultivar. The soil type was a Cisne silt loam (mollic albaqualf). Corn yields were regressed on the K concentration (%K) of whole plants that averaged 25 and 76 cm in height, respectively, and upon the average K concentration of the fifth, sixth, and seventh leaves at early tassel. Co-efficients of multiple determination (R²) for the quadratic equations were 0.71, 0.74, and 0.78, respectively. The critical K percentage (the percent K resulting in maximum predicted yield) for whole corn plants 25 cm in height was determined to be 3.98; for plants 76 cm in height, it was 3.90. The critical K percentage for the average of the fifth, sixth, and seventh leaves was 1.80%. When corn yield was regressed upon K uptake of plants 25 and 76 cm in height, R² values were 0.63 and 0.60, respectively. The K content for the maximum predicted yield when corn plants averaged 25 and 76 cm was 0.094 and 0.674 g/plant, respectively. Since the critical K percentage varied with the stage of plant development, critical percentages established for one stage of growth should not be used for diagnosing plant nutrition problems at other stages of the corn plant's development.